The present invention relates to a method and apparatus for managing the electronic lock of a radio telephone. More particularly, it relates to a method and apparatus for preventing the unauthorized use of the telephone as well as the inadvertent or intentional tampering with the electronic locking device.
Subscribers to telephone service are often charged by the operator of the telephone system for each minute that the telephone is in use, and additional fees per minute of use may also be charged for "long distance" calls. This is particularly true for special purpose telephones such as mobile radio telephones. Accordingly, it is often important to limit operational access of unauthorized persons to a telephone.
The nature of the use of telephones and particularly of mobile radio telephones is such that rigorous control of access to the telephone instrument is difficult to ensure. Often, the goal of limiting access to unauthorized personnel is in direct conflict with a goal of allowing ease of access to authorized personnel. For example, mobile telephones are often installed in automobiles to permit use of the telephone system while driving. However, the authorized user of the telephone is frequently not the only person with access to the automobile. Parking attendants, automobile service personnel and persons borrowing an automobile generally have to be given access to the interior compartment of an automobile and thus have access to a mobile telephone located therein. Likewise, land based telephones must frequently be placed in locations where rigorous control of access to the dialing apparatus of such telephones is difficult to achieve. A telephone installed in a public area may be convenient for authorized users but, at the same time, is accessible to unauthorized persons.
The use of both physical and electronic locks to control the use of telephones is well known. Physical locks, which conventionally are engaged and disengaged by means of a key or combination, mechanically impede a would-be user from obtaining access to a portion of the telephone instrument necessary for dialing.
Telephone systems which utilize a key or other physical device to lock and unlock the telephone instrument require the telephone user to carry the key whenever use of the telephone is desired. An authorized user of a telephone who, for whatever reason, does not have the unlocking key in his possession is denied the ability to place telephone calls.
Electronic lock systems generally obviate the need for carrying a key because such systems generally can be locked by activation of a single switch or button and are unlocked by the execution of the correct unlocking sequence. Other known electronic locks automatically lock the controlled device after each use. However, such electronic systems can often be accidentally locked or locked by unauthorized persons, by the mere activation of a simple locking switch without any knowledge of the operating code.
Electronic locks are known in which telephone dialing may be inhibited by the activation of a switch or button on the telephone instrument. When the locking button or switch is activated, the control circuits in the telephone instrument inhibit dialing by not transmitting the dialing signals necessary to establish communication between the telephone instrument and the telephone network. Frequently, such electronic locks may be unlocked by performing an unlocking sequence consisting of entering an unlock code comprising a predetermined code sequence. If the correct code sequence is input, the control circuit removes the inhibit and enables the transmission of the dialing signals. Electronic locks for telephone instruments of this type are disclosed in U.S. Pat. No. 4,099,033 issued to Murray on July 4, 1978; U.S. Pat. No. 4,314,108 issued to Shauvit on Feb. 2, 1982; and United Kingdom Patent Application No. 2,086,188 by Feuell filed May 6, 1982.
If a lock is accidentally locked, or tampered with, an authorized user of the mobile telephone who does not know the unlocking sequence will be denied use of the telephone. Additionally, an authorized user who mistakenly believes that he knows the unlocking sequence may intentionally activate the locking mechanism and henceforth be unable to unlock the system, possibly at the expense of an expensive service call to open the instrument for the purpose of reprogramming the locking sequence.
It is therefore an object of the present invention to obviate these and other problems in known electronic locking systems and to provide a novel method and apparatus for managing the use of an electronic lock, particularly for mobile radio telephones.
It is another object of the present invention to provide a novel method and apparatus for controlling the use of telephone instruments without the use of a key.
It is yet another object of the present invention to provide a novel method and apparatus for ensuring the correctness of the unlocking sequence prior to engaging an electronic lock.
These and many other objects and advantages of the present invention will be apparent to one skilled in the art from the claims when read in conjunction with the appended drawing.